Illumination optical system and exposure apparatus using the same

ABSTRACT

An illumination optical system for illuminating an illuminated surface using light from a light source includes a first diffraction optical element upon which the light from the light source is incident, and a second diffraction optical element upon which the light from the light source is incident, wherein the light from the first diffraction optical element forms a first part of an illumination distribution on a predetermined surface that substantially has a Fourier transform relationship with the illuminated surface, and the light from the second diffraction optical element forms a second part of the illumination distribution.

TECHNICAL FIELD

The present invention relates to illumination optical systems andexposure apparatuses using the same, and particularly to an illuminationoptical system that handles polarization and an exposure apparatus thatexposes an object, such as a single crystal substrate for asemiconductor, a glass plate for a liquid crystal display.

BACKGROUND ART

As a semiconductor device becomes finer, an exposure wavelength used ina semiconductor exposure apparatus becomes shorter down to a KrF laser(with a wavelength of 248 nm), an ArF laser (with a wavelength of 193nm), and a F₂ laser with a wavelength of 157 nm. At the same time, theNA of a projection optical system becomes higher up to 0.90 in anordinary atmosphere, and beyond 1.2 for a projection optical system ofan immersion type exposure apparatus.

The fine patterning of a semiconductor device is a major factor thatsupports the dynamics of the semiconductor industry, and the generationis swiftly changing from the age that required a resolution of 0.25 μmat 256 MDRAM to 180 nm, 130 nm and further to 100 nm and beyond. In theage of the lithography using the i-line (365 nm), they didn't realizethe resolution less than the wavelength. However, the KrF, having awavelength of 248 nm, has been applied to the critical dimension of 180nm down to 130 nm. The age that practically uses the resolution lessthan the wavelength has really arrived through the progress of resistand the use of results out of resolution enhancement technologies (RET),etc. Various RET would reduce the critical dimension to one-third of thewavelength in line and space patterns.

However, RET often has pattern-induced limits, and therefore, the royalroad to the improvement of resolution is, after all, to make thewavelength short while improving the NA of a projection optical system.Recently, a minute imaging analysis emphasizes considerations ofparameters that have been ignorable in the past, such as flare, and thepolarization due to the property of the light as electromagnetic waves.

Among them, the issue of polarization has gradually had a great impactas a projection optical system's NA becomes larger. The issue thatpolarization presents is such that when two rays intersect each other,they don't interfere with each other if the two rays' polarizeddirections are orthogonal to each other. If two rays are symmetricallyarranged to the optical axis, the angle of the optical axis with one raybecomes 45°. The NA close to 0.71 causes a pair of rays to satisfy thisorthogonal condition. Therefore, a current projection optical systemhaving more than 0.80 already met the condition in which the imagingrays do not interfere with each other in the aerial image.

The effect of this orthogonal condition becomes more prominent in animmersion type exposure apparatus, because even if the orthogonalcondition is present in the aerial image obtained in the air, nitrogen,or helium circumstances (hereinafter called dry), an angle θ_(PR) thatthe light entering a resist having a refractive index of n_(PR) at anangle θ_(o) has in the resist is expressed as follows:sin θ_(o)=n_(PR) sin θ_(PR)  (1)The angle θ_(PR) thus becomes smaller than θ_(o), and does not satisfythe orthogonal condition in the resist.

Usually, since the refractive index of the resist at a wavelength of 193nm is about 1.7. If θ_(PR) becomes 45°, the right-hand side of theequation (1) becomes 1.7×sin 45°=1.20, which is more than 1. Therefore,θ_(PR) 45° condition never exists in the dry case.

However, in the immersion exposure that fills with liquid the spacebetween a resist and a projection optical system, the refraction effectis greatly reduced, and θ_(PR) can be 45°.

Some solutions for this issue have been proposed which control thepolarization of an illumination optical system and maintain the contrastof an image formed by a projection optical system. (See, for example,Japanese Patent Applications, Publication Nos. 8-008177, 4-366841,5-088356, 5-090128,6-124872, 6-181167, and 6-188169.)

In order to expose a pattern with a high resolution, RET takes a measureto control an angular distribution for illuminating reticles and toconstruct an optimal illumination optical system. Various proposed lightsource shapes, such as quadruple, dipole, sextuple as well as theconventional simple annulus contribute to enlarge the exposure latitudeand the depth of focus. A CGH (Computer Generated Hologram) inserted asa diffraction optical element into an illumination optical systemprovides flexibility to form various light source shape requirements,thus making an important contribution to the progress of opticallithography. See, for example, Japanese Patent Applications, PublicationNos. 2001-284212 and 11-176721.

However, the control of polarization that has become especiallyconspicuous for an immersion type exposure apparatus, and theflexibility of the illumination optical system are newly requiredissues.

An illumination optical system should be suitable for a high NA opticalsystem, such as a projection optical system used in an immersion typeexposure apparatus, while reconciling polarization to the optical systemhaving a diffraction optical element.

DISCLOSURE OF INVENTION

An illumination optical system according to one aspect of the presentinvention for illuminating an illuminated surface using light from alight source includes a splitting optical system for splitting the lightfrom the light source into light incident upon a first diffractionoptical element, and light incident upon a second diffraction opticalelement, a first polarization unit for adjusting a polarization state ofthe light from the first diffraction optical element, a secondpolarization unit for adjusting a polarization state of the light fromthe second diffraction optical element, and an integrating opticalsystem for integrating the light from the first diffraction opticalelement with the light from the second diffraction optical element, andfor introducing integrated light into the illuminated surface.

Other features and advantages of the present invention will be apparentfrom the following description given in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a diagram showing an exposure apparatus of a first embodiment.

FIG. 2 is a view for explaining the principle that controls theflexibility of an effective light source and a polarization state.

FIG. 3A is a view showing a light intensity distribution formed by a CGH6 a. FIG. 3B is a view showing a light intensity distribution formed bya CGH 6 b. FIG. 3C is a view showing an example of quadrupleillumination.

FIG. 4A is a view showing a light intensity distribution formed by a CGH6 a. FIG. 4B is a view showing a light intensity distribution formed bya CGH 6 b. FIG. 4C is a view showing an example of a dipoleillumination.

FIG. 5A is a view showing light intensity distribution formed by a CGH 6a. FIG. 5B is a view showing a light intensity distribution formed by aCHG 6 b. FIG. 5C is a view showing an example of a dipole illuminationorthogonal to FIG. 4C.

FIG. 6A is a view showing a light intensity distribution formed by a CGH6 a. FIG. 6B is a view showing a light intensity distribution formed bya CGH 6 b. FIG. 6C is a view showing an example of an illumination withno polarization in the central part and tangential polarization in theperiphery.

FIG. 7A is a view showing a light intensity distribution formed by a CGH6 a. FIG. 7B is a view showing a light intensity distribution formed bya CGH 6 b. FIG. 7C is a view showing an example of an annularillumination with tangential polarization in ±45° directions.

FIG. 8 is a view showing part of an illumination optical system of asecond embodiment.

FIG. 9A is a view showing a light intensity distribution formed by aCGH. FIG. 9B is a view showing a light intensity distribution formed bya CGH. FIG. 9C is a view showing a light intensity distribution formedby a CGH. FIG. 9D is a view showing a light intensity distributionformed by a CGH. FIG. 9E is a view showing an example of an annularillumination with tangential polarization.

FIG. 10 is a view showing part of an illumination optical system of athird embodiment.

FIG. 11A is a view showing a light intensity distribution formed by aCGH. FIG. 11B is a view showing a light intensity distribution formed bya CGH. FIG. 11C is a view showing an example of an illumination withnon-polarization in ±45° directions around a cross-shapednon-illuminated part, and with tangential polarization in ±90°directions.

FIG. 12 is a diagram showing an immersion type exposure apparatus of afourth embodiment.

FIG. 13 is a view showing an immersion type exposure apparatus of afifth embodiment.

FIG. 14 is a device manufacturing flow.

FIG. 15 is a figure showing the wafer process in FIG. 14.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

First Embodiment

FIG. 1 shows a structure of an illumination optical system used in anexposure apparatus of a first embodiment.

An excimer laser 1 is used for the exposure apparatus as a light source.It provides linearly polarized light. In order to control thepolarization state of the whole illumination optical system, thisembodiment utilizes the polarization characteristics that the laseroriginally possesses.

The excimer laser is shaped by a beam-shaping optical system 2 having abeam expander, etc. such that it may be adjusted for the optical systemsthat follow, and then, enters a beam splitter 3 as a splitting opticalsystem, being split into two. Actually, the laser is located distantfrom the exposure apparatus for installation convenience, and light isoften guided a long way up to the beam splitter via a beam deliverysystem. Because of the guidance from the laser to the beam splitter, ifthe laser beam enters the beam splitter 3 as an s-polarized light, thecoating of the beam splitter may be set such that s-polarized light issplit with an intensity ratio of 1:1.

If the laser is of non-polarization, a polarization beam splitter isused for the beam splitter 3. Even in this case, the split rays becometwo linearly polarized lights that are orthogonal to each other with thealmost equal intensity. In other words, the splitting operation almostequalizes the intensity of the optical path of the split light as alinear polarization state.

The light having transmitted the beam splitter 3 is reflected on amirror 4. The split beams enters, through separate optical paths,polarization units Sa and 5 b, and CGH 6 a and 6 b, respectively. Adescription of their operations will be given later, but in summary eachoptical path is independently provided with the polarization unit foradjusting the polarization state and the CGH for forming an effectivelight source shape. That is, it is important in the instant embodimentthat a first optical system that includes the polarization unit 5 a andthe CGH 6 a, and a second optical system that includes the polarizationunit 5 b and the CGH 6 b are set on different optical paths,respectively.

Then, the beams go through collimators 7 a and 7 b, and enter a beamintegrating optical system 8, thus arriving at an integrator 10. Theintegrator 10 is a fly's-eye lens, and forms a plurality of secondarylight sources at its exit surface.

The illumination optical system after the integrator 10 includescondensers 11 a and 11 b, a slit 12, a condenser 13, a mirror 14, and acollimator 15, and illuminates a reticle (or a mask). In order tocontrol an exposure light intensity, a beam splitter 17 is arrangedbetween the condensers 11 a and 11 b in the instant embodiment, andtakes out light so as to detect a light intensity given by theillumination optical system. A photodetector 18 is movably arranged onthe reticle surface, and detects the light intensity on the reticlesurface.

The light having passed through the reticle 16 is projected and imagedonto a wafer 22 via a projection optical system 21. The wafer 22 is seton a wafer chuck 23, and the wafer chuck 23 is installed on a waferstage 24. A detecting system 25 has a detector for detecting a lightintensity, and is mounted on the wafer stage. The detecting system 25detects the light intensity that has passed through the wholeillumination and projection optical systems.

While this embodiment arranges the photodetector on the reticle surfaceor a position corresponding to the wafer surface, the detector can beplaced at a location corresponding to the pupil position to perform asimilar function.

FIG. 2 shows the method of forming the effective light source requiredfor an exposure apparatus and a principle of controlling thepolarization state. It shows the relationship between the CGH 6 a and 6b and the integrator 10. The embodiment in FIG. 1 uses CGH 6 a and 6 bto form a necessary effective light source distribution over theintegrator 10, while separating optical paths for 6 a and 6 b andindependently controlling the polarization on each optical path. Thus,this embodiment can effectively use the light, control polarization, andefficiently forms a whole illumination optical system. This embodimentuses a fly's-eye lens as an integrator, and forms an effective lightsource distribution at its incident plan. The similar effective lightsource distribution is formed at the exit plane of the fly's eye lens.In short, the CGH 6 a and 6 b are arranged at a place that substantiallyhas a Fourier transform plane (pupil conjugate plane) to the reticle,and used to form an effective light source distribution at the incidentplane of the fly's eye lens. The integrator that uses an optical pipe asan internal reflecting mirror can provide similar effects.

FIGS. 3A to 3C are views showing the principle, for example, of thequadruple illumination as an effective light source on the X and Y axes.As illustrated in FIG. 3C it is desirable that the effective lightsource on the Y-axis has a lateral polarization, and the effective lightsource on the X-axis has a longitudinal polarization. The CGH 6 a makesa distribution on the X-axis of the element 10 like a 61 a 1 and 61 a 2as shown in FIG. 3A. The polarization state is a linear polarization inthe longitudinal direction. On the other band, the CGH 6 b makes adistribution on the Y-axis of the element 10 like a 61 b 1 and 61 b 2 asshown in FIG. 3B. The polarization state is a linear polarization in thelateral direction. The same CGH 6 a and 6 b can be used, but rotated by90° when arranged. The polarization controlling elements 5 a and 5 bcontrol the polarization direction, and use a rotational λ/2 plate andthe like. Since the polarization controlling elements 5 a and 5 b areseparate from each other, the polarization state of lights that havepassed the CGH 6 a and 6 b can be controlled independently to lead themto the integrator 10. The resultant effective light source is shown inFIG. 3C, by which illumination is materialized whose polarizationdirection is a tangential direction orthogonal to a line that connectsthe center.

The effective light source having passed the same CGHs, i.e., the 61 a 1and 61 a 2, and 61 b 1 and 61 b 2 can be set by the CGHs to have thesame light intensity, but light on the 61 a system and that on the 61 bsystem need to be made equal in terms of the light intensity. An NDfilter for light intensity adjustment if provided in each optical pathwould provide proper control over the exposure ray width. Since anactual adjustment quantity is minute, a stop that has a variablediameter may be put in the optical path before entering the CGH formutual adjustments. A detailed description of the light intensityadjustment function will be given later.

The CGH works effectively for a dipole illumination. FIG. 4 shows adipole illumination formed on the X-axis. Like FIG. 3, the CGH 6 a makesa distribution on the X-axis of the element 10 like 62 a 1 and 62 a 2 asshown in FIG. 4A. The polarization state is linear polarization in alongitudinal direction. On the other hand, the CGH 6 b also makes adistribution on the X-axis of the element 10 like a 62 b 1 and 62 b 2 asshown in FIG. 4B. The polarization state is linear polarization in alongitudinal direction. The same CGH 6 a and 6 b can be used in the samearrangement. The operations of the polarization controlling elements 5 aand 5 b provide the same polarization state to lights that have passedthe CGH 6 a and 6 b. The polarization controlling elements 5 a and 5 bmerely rotate polarization direction and do not reduce the lightintensity. Therefore, the dipole illumination has the same efficiency asthe quadruple illumination in FIG. 3.

FIG. 5C is a view of a dipole illumination rotated by 90° from that ofFIG. 4C. The CGH 6 a makes a distribution on the Y-axis of the element10 like 63 a 1 and 63 a 2 shown in FIG. 5A. The polarization state islinear polarization in the lateral direction. On the other hand, the CGH6 b also makes a distribution on the Y-axis like 63 b 1 and 63 b 2 shownin FIG. 5B. The polarization direction is also a lateral direction. Thesame CGH 6 a and 6 b as FIG. 4C can be used although rotated by 90° whenarranged. Also in this case, the operations of the polarizationcontrolling elements 5 a and 5 b provide the light having passed the CGH6 a and 6 b to the same polarization state. The illumination efficiencyis the same as that of the quadruple illumination of FIG. 3C.

The CGH can easily form a more complicated effective light distribution.FIG. 6C shows one embodiment that forms a effective light source havinga central part with no polarization, and a peripheral part with atangential polarization. In FIG. 6A, the intensity at the centralportion 64 a of the effective light source formed by the CGH 6 a is halfthe intensity of the peripheral portions 64 a 1 and 64 a 2, and thepolarization direction is adjusted to be a longitudinal direction. Asshown in FIG. 6B, the intensity at the central portion 64 b of theeffective light source formed by the CGH 6 b is half the intensity ofthe peripheral portions 64 b 1 and 64 b 2, and the polarizationdirection is controlled to be a lateral direction. The intensitydifference is illustrated in colors. If they are synthesized, aneffective light source has a uniform intensity distribution, in whichthe central part has no polarization, and only the periphery has atangential polarization as shown in FIG. 6C.

The polarization direction is controllable in not only longitudinal andlateral directions, but any arbitrary direction, if, for example, apolarization unit 5 includes a rotational λ/2 plate, by controlling aset angle of the λ/2 plate. FIG. 7C is an example of an annularillumination that has a tangential polarization state by combining ±45°polarization directions. One CGH 6 a forms effective light sources 65 a1 and 65 a 2 in the +45 direction as illustrated in FIG. 7A, and theother CGH 6 b forms effective light sources 65 b 1 and 65 b 2 in the −45direction as illustrated in FIG. 7B. The superimposed light sources formthe annular illumination on the integrator 10 in the ±45° polarizationdirections.

An effective light source distribution can also be formed as shown inFIGS. 11A to 11C, which has a cross-shaped non-illuminated part in thecenter, no polarization in the ±45° directions in its periphery, and atangential polarization in the 0° and ±90° directions.

It is also possible to easily realize a combination of a morecomplicated effective light source distribution and polarizationdirections.

A different effective light source is variable by exchanging the CGH inaccordance with a light source shape. For example, the CGH need beexchanged between ⅔ and ¾ annular illuminations. An outer diameter ofthe effective light source, which is an important parameter, needs to bedetermined in the annular illumination. This corresponds to control overan annulus's size (or diameter) formed on the integrator 10, and a beamintegrating optical system 8 plays this role. The element 8 has azooming function to change a size of the annulus as well as a size ofanother effective light source on the integrator 10.

Of course, the illumination optical system needs to form a normalcircular illumination shape. This needs an adjustment of so-called σ(=NA of an illumination optical system's reticle side/NA of a projectionoptical system's reticle side). Thus, a variable beam diameter on theintegrator's incident surface is needed to change a shape of the lightintensity distribution on the illumination optical system's pupilsurface (which has a Fourier transform relationship with the reticlesurface or is conjugate with the integrator 10's exit surface). Thezooming function of the element 8 meets this requirement of variability.A CGH 6 that forms a circular pattern is used for the integrator increating a circular shape of the effective light source. Alternatively,an optical system using an ordinary lens may be inserted in an opticalsystem as a turret, utilizing the circular shape. In some cases, thesame light intensity of linearly polarized rays that are orthogonal toeach other is required in order to attain the two dimensional CDcontrol.

As discussed, the embodiment remarkably improves the flexibility of theillumination optical system by an exchange of the CGH as a diffractionoptical element and the zooming function, and can control thepolarization direction.

A provision of many kinds of CGHs would take tune for exchange andincrease the cost. The number of necessary CGHs can be reduced if eachCGH has a rotational function. For example, suppose the illustrativedipole illuminations shown in FIGS. 4C and 5C where both dipoleilluminations are different in that the same shape is simply rotated by90° between FIGS. 4C and 5C. A description will now be given of FIG. 4Cby referring to the system's numerals in FIG. 1. The CGHs 6 a and 6 bmay be exactly the maine since they form the same effective light sourceshape on the integrator 10. In other words1 the same CGH can be used.

The dipole in FIG. 5C is the dipole shape of FIG. 4C rotated by 90°. Inthis case, the CGH used in the system of FIG. 4C may be rotated 90°.Accordingly, if the CGH itself has a rotation function, there is no needto exchange the CGH when changing from the effective light source shownin FIG. 4C to that of FIG. 5C. If each dipole structure in the quadruplein the system shown in FIG. 3C is equivalent to that shown in FIGS. 4Cand 5C, or if the portions 61 a 1 and a 2 in FIG. 3A are equivalent tothe portions 62 a 1 and a 2 in FIG. 4A, and the portions 61 b 1 and b 2in FIG. 3B are equivalent to the portions 63 b 1 and b 2 in FIG. 5B, twoCGHs of the same type are needed to create the effective light sourceshown in FIGS. 3C, 4C and 5C. In this case, “equivalent” means the sameshape, ignoring the directionality.

CGHs of multiple types may be necessary to form other types of effectivelight source shapes so that each CGH is inserted into and removed fromthe optical path. For example, the CGHs may be placed on a turret andswitchably inserted into the optical path.

While the above embodiment varies the polarization state by arranging apolarization unit at each of the multiple optical paths, all or part ofthem may be omitted if there is no need to change the polarization.

Second Embodiment

FIG. 8 is a view showing a part of an illumination optical system in anexposure system of a second embodiment. In order to control polarizationmore minutely than the first embodiment, the illumination optical systemincludes an optical path splitting section that is adapted to quadrisectan optical path of the light from a light source which has exited thebeam shaping optical system 2, so as to control, for example, not onlylongitudinal and lateral directions but also ±45° directions. Theoptical path is, at first, split into two by the beam splitter 3, andthen each of them is further split into two by beam splitters 31A and31B, thus forming four beams. The respective beams are provided withpolarization units 5A to 5D, CGH 6A to 6D, and four collimators (notshown). The illumination optical system after the optical pathintegrating element 8 has the same configuration as that of theembodiment shown in FIG. 1, and a description thereof will be omitted.

FIGS. 9A to 9E are an exemplary annular illumination that has atangential polarization direction in the system of FIG. 8. Since fourpolarization directions are controllable along four optical paths, theinstant embodiment forms annular illumination by combiningfour-directional linearly polarized rays of 0°, 90°, and ±45°. In otherwords, the first optical pat forms poitions 61A1 and A2 in the effectivelight source in the 0° polarization direction. The second optical pathforms portions 61B1 and B2 in the effective light source in the 90°polarization direction. The third optical path forms portions 61C1 andC2 in the effective light source in the +45° polarization direction. Thefourth optical path forms portions 61D1 and D2 in the effective lightsource in the −45° polarization direction. Thus, the whole annularillumination is formed. A CGH is used to make any effective lightsource. The linearly polarized light is arranged at an outer peripheryof the effective light source in a tangential direction.

While this embodiment uses a structure of two CGHs of two kinds toconform to a fly's eye shape, two similar CGHs of the same type may bearranged in each optical path while rotated by 45° relative to eachother, when each CGH is expected to form a shape of completely cutting adonut in the effective light source.

Of course, when the four-directional polarization directions are notneeded, it is possible to use adjustment by the polarization unit 5 toarrange beams from all the CGHs into the same polarization direction,two directions or three directions. Which polarization state to choosedepends upon the characteristics of a pattern to be exposed, but thisembodiment can set up the CGHs for the optimum condition with ease.

Third Embodiment

The third embodiment describes a method for detecting or adjusting thelight intensity in the exposure apparatus of the embodiments 1 and 2.

One issue in the illumination optical system that handles thepolarization state is the way of detecting the light intensity. Theoptical system shown in FIG. 1 arranges the beam splitter 17 after theintegrator 10, monitors the light intensity of light reflecting at 17 bya light integrator unit L1 as a monitor section, and controls theexposure dose. However, the beam splitter 17 is disposed obliquely tothe optical axis of the illumination optical system, and the reflectancenaturally varies depending upon polarizations. The illumination opticalsystem of the embodiment in FIG. 1 handles the complex selection of thepolarization directions, i.e., longitudinal and lateral directions as inFIGS. 3C, 4C and 5C, and ±45° directions as in FIG. 6C or other angles,and has difficulties in correctly monitoring the energy that theillumination optical system provides for the reticle by using a lightintensity detecting system having polarization characteristics.

In some cases, it is necessary to balance the light intensities amongoptical paths. For example, a difference between the intensity of theeffective light source on the X-axis of the system in FIG. 3C and thatof the effective light source on the Y-axis causes a difference incritical dimension between the exposed longitudinal and lateral lines.This difference in light intensity stems from the performance of thebeam splitter 3 and the individual differences of the CGHs themselves,and it may be regarded as a difference between the optical paths afterbeing split by the element 3.

On the other hand, the dipole system like FIG. 4C or FIG. 5C forms thesame image of an effective light source, the same polarizationdirections between the split optical paths, unlike FIG. 3C, and thusrequires no light intensity matching between the split optical paths.

Therefore, such an effective light source as FIG. 3C requires anadjustment of light intensities between the split optical paths beforean exposure, The present embodiment detects and adjusts the lightintensities between the split optical paths by using a movable detector18 that is arranged at a position conjugate to the reticle surface aswell as calibrating the light integrator L1's value.

Instead of the detector 18 disposed at a position conjugate to thereticle surface, a photoelectric detector 25 that is disposed on a waferstage, and can detect a light intensity at a position conjugate to thewafer position, may serve as similar functions, i.e., a detection oflight intensities between split optical paths, and necessary adjustmentsand light integrator L1's calibration. Whether the detector 18 is usedor the photoelectric detector 25 is used, the results are similar, butwhen the projection optical system 21 has polarization characteristics,use of the photoelectric detector 25 that detects at the wafer side willprovide more accurate controlling of the exposure dose. One exemplaryprojection optical system 21 having polarization characteristics is acatadioptric optical system.

A description will now be given of light intensity adjustment for eachoptical path and a procedure for determining a light integrator'scontrolling conditions. At first, the illumination optical system'spolarization state controlling means 5, the CGH 6 and the optical pathintegrating element 8's zoom are set to the exposure conditions.

Each optical path that is split by the beam splitter 3 is provided witha shutter that can independently shield the light of the optical pathand a light intensity adjusting function. In detecting the lightintensity of each optical path, only the light on a first optical pathis allowed to pass, and the remaining light is shielded. A memory (notshown) stores a light intensity detected by the detector 18 orphotoelectric detector 25 in this state and a value L1 at this time. Forconvenience of explanation, it is assumed that the photoelectricdetector 25 detects the light intensity.

Then, a second optical path, and depending on structure, other opticalpaths are measured in a similar manner. First, a ratio between theoutput values LI and the element 25 are calculated, and a ratio betweena LI controlled value and an actual light intensity is determined. Sincethe polarization state changes according to the illumination method, thevalue of this ratio needs to be calibrated again each time theillumination method (illumination mode) changes.

After that, a light intensity balance is adjusted for each optical path.As described, this step may be omitted if there is no light intensitybalance required as in the dipole illumination shown in FIGS. 4C and 5C.

In the light intensity adjustment, the optical path having a minimumvalue is treated as a reference value among all the light intensitiesdetected by the photoelectric detector 25, and the light intensity ofeach of other optical paths is adjusted to conform to this lightintensity. A light intensity adjusting means provided on each opticalpath adjusts the light intensity. The light intensity adjusting meansmay use a method using an ND filter, a method that controls the diameterof a beam incident upon the CGH, etc. The method for controlling thediameter of a beam incident upon the CGH takes advantage of the factthat even if the diameter of an incident beam changes, the image formedon the integrator does not change. An actual adjustment of the lightintensity ratio does not require so wide a range if the film of aninitial beam splitter is correctly made. Accordingly, use of a means forvarying a diameter such as an iris stop provides continuous adjustments.An ND filter requires several kinds of filters to be prepared forswitching, and the space for switching, whereas the iris stop isadvantageously space-saving. The iris stop can serve as a shutter. FIG.10 shows a structure of an optical path having a light intensityadjustment function. It is an example of an iris stop 28 that serves asa shutter, arranged before a rotational CGH 6 and the rotational λ/2polarization unit 5. Since the light diffracts and spreads after passingthrough the CGH 6, the iris stop need be arranged before the CGH 6, butits position can be replaced with a position of the polarization unit 5.The light intensity adjusting means does not have to be arranged foreach optical path, but may be provided only on some optical paths.

When the above light intensity adjusting means provides necessaryadjustments to the light intensity ratio among optical paths andcorrelates the light intensity detected at the light integrator with theexposure light intensity, the exposure is ready to start.

This embodiment is applicable to exposure apparatuses of all the otherembodiments.

As discussed, the invention of the above embodiment splits the opticalpath, and independently provides a CGH and a polarization element toeach split optical path, thus controlling a polarization direction, andforming an efficient and respondent illumination optical system. Theexposure optimized in the polarization state and the effective lightsource shape suitable for an exposed pattern greatly improves theresolution. The illumination optical system of the above embodiment,converts the light incident upon the CGH into a pattern on theintegrator and polarized light by an element like the λ/2 plate, andthus achieves high efficiency with great flexibility. Use of the dipoleillumination that controls the polarization with the illuminationoptical system of the above embodiment will enable an exposure apparatusto realize the high resolution performance without degrading theefficiency of the intended effective light source distribution.

Fourth Embodiment

FIG. 12 is a view showing the structure of an immersion type exposureapparatus according to the instant embodiment, and a direction verticalto the paper surface (the z direction) corresponds to the actualperpendicular direction. Like elements in the first embodiment aredesignated by the same reference numerals.

In the embodiment, the exposure light from an illumination apparatus ISilluminates a reticle 16, and a pattern on the reticle 16 is reduced,projected and transferred by a projection optical system 21′ onto awafer 22 as a photosensitive substrate to which a resist is applied.Here, the illumination apparatus IS has a structure similar to the firstembodiment, and includes the laser 1 as a light source, and elementsfrom the beam shaping optical system 2 to a collimator 15 in FIG. 1.

The immersion type exposure apparatus according to the instantembodiment is a so-called step-and-scan type exposure apparatus, inwhich the reticle 16 and the wafer 22 are synchronously scanned forexposure.

A projection optical system barrel 77 constitutes a part of theprojection optical system PL, and is a member arranged closest to thewafer 22. 79 a is a liquid supplying apparatus, which supplies liquid toa space between a projection optical system barrel 77 and the wafer W,thus forming a liquid film.

79 b is a liquid collection apparatus, which collects liquid via anozzle 71 b and a pipe 73 b.

The liquid used for an immersion type exposure apparatus is required tomeet the condition that it should absorb as little exposure light aspossible and let it transmit. An immersion type exposure apparatus thatuses the ArF or KrF excimer laser as a light source can use pure wateras the immersion liquid.

In the embodiment, the illumination optical system splits the opticalpath into two, puts a CGH and a polarization unit at least on oneoptical path, and integrates the two on the integrator's incidentsurface. Therefore, an intended shape of the effective light source andthe polarization control are easily feasible, and the resolutionperformance is not affected very much even if imaging lights areorthogonal within a resist.

Fifth Embodiment

FIG. 13 is a schematic view of the exposure apparatus of a fifthembodiment. The first to fourth embodiments use only one laser as alight source. On the other hand, the embodiment uses two lasers, i.e.,lasers 1 a and 1 b, as a light source.

The first embodiment split the beam exiting the beam shaping opticalsystem 2 by the beam splitter 3 into two beams. On the other hand, theinstant embodiment uses deflection mirrors 30 and 40, introducing thebeams exiting the beam shaping optical systems 2 a and 2 b into thepolarization units 5 a and 5 b. Elements in FIG. 12, which are similarelements in first embodiment are designated by the same referencenumerals.

When respective beams from the lasers 1 a and 1 b enter the deflectionmirrors 30 and 40, their polarization directions are preferably parallelto each other.

While this embodiment makes the light source of two lasers, the presentinvention is not limited to this embodiment, and the light source mayinclude three or more lasers. For example, the light source in thesecond embodiment may include four lasers.

Further, the instant embodiment's illumination apparatus (with elementsfrom the lasers la and lb to the collimator 15) may be used for theimmersion type exposure apparatus of the fourth embodiment.

While the above first to fifth embodiments use a so-called step-and-scantype exposure apparatus as an exposure apparatus, a step-and-repeat typeexposure apparatus may be used instead.

Sixth Embodiment

A description will now be given of an embodiment of a fabrication methodfor devices (semiconductor devices, liquid crystal display devices,etc.) using the above exposure apparatus.

FIG. 14 shows a device fabrication flowchart. Step 1 (circuit design)designs a semiconductor device circuit. Step 2 (reticle fabrication)forms a reticle having a designed circuit pattern. Step 3 (waferpreparation) manufactures a wafer as a plate (or an object to beprocessed) using materials such as silicon. Step 4 (wafer process),which is also referred to as a pretreatment, forms actual circuitry onthe wafer through the photolithography technique using the reticle andwafer. Step 5 (assembly), which is also referred to as a posttreatment,forms into a semiconductor chip the wafer formed in Step 4 and includesan assembly step (e.g., dicing, bonding), a packaging step (chipsealing), and the like. Step 6 (inspection) performs various tests forthe semiconductor device made in Step 5, such as a validity test and adurability test. Through these steps, a semiconductor device is finishedand shipped (Step 7).

FIG. 15 is a detailed flowchart of the above wafer process. Step 11(oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms aninsulating film on the wafer's surface. Step 13 (electrode formation)forms electrodes on the wafer by vapor disposition. Step 14 (ionimplantation) implants ions into the wafer. Step 15 (resist process)applies a resist (or a photosensitive material) onto the wafer. Step 16(exposure) uses the above described exposure apparatus to expose acircuit pattern on the reticle onto the wafer. Step 17 (development)develops the exposed wafer. Step 18 (etching) etches parts other than adeveloped resist image. Step 19 (resist stripping) removes disusedresist after etching. These steps are repeated, and circuit patterns areformed on the wafer.

Use of the fabrication method according to the instant embodiment makesit possible to fabricate highly integrated devices that were difficultto realize.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the claims.

This application claims a foreign priority based on Japanese PatentApplication No. 2003-321419, filed Sep. 12, 2003, which is herebyincorporated by reference herein.

1. An illumination optical system for illuminating an illuminatedsurface using light from a light source, said illumination opticalsystem comprising: a splitting optical system for splitting the lightfrom the light source into light incident upon a first diffractionoptical element, and light incident upon a second diffraction opticalelement; a first polarization unit for adjusting a polarization state ofthe light from the first diffraction optical element; a secondpolarization unit for adjusting a polarization state of the light fromthe second diffraction optical element; and an integrating opticalsystem for integrating the light from the first diffraction opticalelement with the light from the second diffraction optical element, andfor introducing integrated light into the illuminated surface.
 2. Anillumination optical system according to claim 1, further comprising anadjusting unit for adjusting a light intensity of the light from thefirst diffraction optical clement, and/or an adjusting unit foradjusting a light intensity of the light from the second diffractionoptical element.
 3. An illumination optical system according to claim 2,further comprising a shielding unit arranged in an optical path of thelight incident upon the first and/or second diffraction opticalelements.
 4. An illumination optical system according to claim 2,further comprising a detector for detecting a light intensity of thelight from the first diffraction optical element and a light intensityof the light from the second diffraction optical element, wherein saidadjusting unit adjusts a ratio between a light intensity of the lightfrom the first diffraction optical element and a light intensity of thelight from the second diffraction optical element.
 5. An illuminationoptical system according to claim 1, further comprising an integratorfor forming a plurality of secondary light sources using the light fromthe light source, wherein said integrating optical system integrates thelight from the first diffraction optical element with the light from thesecond diffraction optical element at an incident surface of theintegrator.
 6. An illumination optical system according to claim 1,wherein said integrating optical system comprises a zooming opticalsystem.
 7. An illumination optical system according to claim 1, whereinsaid first or second polarization unit comprises a rotational λ/2 plate.8. An illumination optical system according to claim 1, wherein thefirst or second diffraction optical element is rotational.
 9. Anillumination optical system for illuminating an illuminated surfaceusing light from a plurality of light sources that includes first andsecond light sources, said illumination optical system comprising: afirst diffraction optical element upon which the light is incident fromthe first light source among the plurality of light sources; a seconddiffraction optical element upon which the light is incident from thesecond light source among the plurality of light sources; a firstpolarization unit for adjusting a polarization state of the light fromsaid first diffraction optical element; a second polarization unit foradjusting a polarization state of the light from said second diffractionoptical element; and an integrating optical system for integrating thelight from the first diffraction optical element with the light from thesecond diffraction optical element, and for introducing integrated lightinto the illuminated surface.
 10. An exposure apparatus comprising: anillumination optical system for illuminating a reticle; and a projectionoptical system for projecting a pattern on the reticle onto a plate,wherein said illumination optical system includes: a splitting opticalsystem for splitting light from a light source into light incident upona first diffraction optical element and light incident upon a seconddiffraction optical element; a first polarization unit for adjusting apolarization state of the light from the first diffraction opticalelement; a second polarization unit for adjusting a polarization stateof the light from the second diffraction optical element; and anintegrating optical system for integrating the light from the firstdiffraction optical element with the light from the second diffractionoptical element, and for introducing integrated light into the reticle.11. An exposure apparatus according to claim 10, further comprising: adetector for detecting a light intensity of the light from the firstdiffraction optical element and a light intensity of the light from thesecond diffraction optical element; and an adjusting unit for adjustinga ratio between the light intensity of the light from the firstdiffraction optical element and the light intensity of the light fromthe second diffraction optical element.
 12. An exposure apparatusaccording to claim 11, wherein the illumination optical system includesa monitoring section for monitoring a light intensity at a positioncorresponding to a surface of the reticle, and calibrates monitoringaccording to an adjustment of balance.
 13. An exposure apparatusaccording to claim 11, wherein the detector detects the light intensityat a position corresponding to the surface of the reticle or a surfaceof the plate.
 14. A device fabrication method comprising the steps of:exposing a plate by using an exposure apparatus; and developing theplate, wherein said exposure apparatus includes: an illumination opticalsystem for illumintating a reticle; and a projection optical system forprojecting a pattern on the reticle onto the plate; wherein saidillumination optical system includes: a splitting optical system forsplitting light from a light source into light incident upon a firstdiffraction optical element and light incident upon a second diffractionoptical element; a first polarization unit for adjusting a polarizationstate of the light from the first diffraction optical element; a secondpolarization unit for adjusting a polarization state of the light fromthe second diffraction optical element; and an integrating opticalsystem for integrating the light from the first diffraction opticalelement with the light from the second diffraction optical element, andfor introducing integrated light into the reticle.
 15. An exposureapparatus comprising: an illumination optical system for illuminating areticle; and a projection optical system for projecting a pattern on thereticle onto a plate, wherein said illumination optical system includes:a first diffraction optical element upon which light is incident from afirst light source among a plurality of light sources; a seconddiffraction optical element upon which the light is incident from asecond light source among the plurality of light sources; a firstpolarization unit for adjusting a polarization state of the light fromthe first diffraction optical element; a second polarization unit foradjusting a polarization state of the light from the second diffractionoptical element; and an integrating optical system for integrating thelight from the first diffraction optical element with the light from thesecond diffraction optical element, and for introducing integrated lightinto the reticle.
 16. A device fabrication method comprising the stepsof: exposing a plate by using an exposure apparatus; and devleoping theplate, wherein said exposure apparatus includes: an illumination opticalsystem for illumintating a reticle; and a projection optical system forprojecting a pattern on the reticle onto the plate; wherein saidillumination optical system includes: a first diffraction opticalelement upon which light is incident from a first light source among aplurality of light sources; a second diffraction optical element uponwhich the light is incident from a second light source among theplurality of light sources; a first polarization unit for adjusting apolarization state of the light from the first diffraction opticalelement; a second polarization unit for adjusting a polarization stateof the light from the second diffraction optical element; and anintegrating optical system for integrating the light from the firstdiffraction optical element with the light from the second diffractionoptical element, and for introducing integrated light into the reticle.